let empty = {};
let point = { x: 0, y: 0 };
let p2 = { x: point.x, y: point.y + 1 };
let book = {
  "main title": "JavaScript", // 属性名包含空格
  "sub-title": "The Definitive Guide", // 和连字符，因此使用字符串字面量
  for: 32,
  author: {
    firstname: "David",
    surname: "flanagan",
  },
};
